The present invention relates to a dry-etching method and apparatus used in a process for producing semiconductors and, particularly, to a dry-etching method and apparatus capable of achieving highly selective etching.
In a conventional dry-etching method, a reaction is triggered by active species from the plasma of a reactive gas. The reaction is promoted by the incident energy of the ions, but reaction anisotropy develops since there is anisotropy in the incident direction of the ions.
In this case, the energy of the incident ions is transferred to the surface of the material to be etched to locally heat that portion, and the etching reaction proceeds very quickly due to the hot spot which is produced by the local heating (see, e.g., Journal of Vacuum Science and Technology, B4, 1986, p. 459). The measurement of the hot spot temperature has been reported in the Journal of Applied Physics, 64, 1988, p. 315. In low-temperature etching technology (Japanese Patent Laid-Open No. 158627/1985, Japanese Patent Laid-Open No. 63291423), the sample is maintained at a very low temperature to suppress the etching caused by the spontaneous reaction of incident particles such as radicals, and the etching reaction is established at the hot spot only in order to achieve realize high anisotropy.
In the conventional dry-etching method, however, hot spots are produced on portions that are desired to be etched as well as on portions that are not desired to be etched due to ions incident from the plasma. Furthermore, the temperature of the hot spots has not been particularly controlled and the hot spot temperature has thus been high. This can cause the etching reaction to proceed even on those portions that are not desired to be etched. Therefore, very highly selective etching is not realized.
In the conventional dry-etching method, furthermore, the temperature of a hot spot is not sufficiently raised on the surface of the material that is to be etched depending upon the combination of ions incident from the plasma and the material that is to be etched. Therefore, the etching rate is small and a sufficiently large selectivity is not obtained. This problem becomes conspicuous particularly when the material to be etched is one that contains heavy atoms such as tungsten (W) and the like.
Moreover, the conventional dry-etching apparatus is not provided with a mechanism for measuring and controlling the hot spot temperature. Therefore, the rate of the etching reaction is not sufficiently controlled, and the selectivity of the etching is small for the materials.